A signal booster or a relay node has been developed/installed to overcome signal loss in a shadow area and to extend a coverage for a signal. For such purposes, the signal boosters can be classified into a fixed type, a nomadic type and a mobile type according to installation purposes and configurations. Moreover, the signal boosters can be sorted by A & F (amplify & forward), D & F (decode and forward), M & F (modulation & forward) and the like depending on whether a separate signal processing is additionally performed. Currently, in IEEE 802.16m, IEEE 802.16mmr, 3GPP LTE/LTE-A and the like, the signal booster or relay node is supported by the corresponding system. Yet, in the conventional communication systems, the fixed A & F signal boosters are mostly popular. This is attributed to the following reasons. First of all, a communication system of a related art does not support a signal booster by itself. Secondly, it is highly possible that a delay time due to a signal transceiving and processing in an booster of a cellular system supposed to mainly support such a bi-directional real-time packet service as a voice service and the like may exceed a limited time determined by the corresponding system. So to speak, when a base station is not aware of a presence or non-presence of installation/use of a signal booster, the A & F signal booster is the most reasonably available signal booster.
In case that a fixed or nomadic signal booster is installed to solve the problem of signal loss in a shadow area, it is able to maintain a fixed uplink transmit power. However, in case that a mobile signal booster is installed, a transmit power of a fixed output causes serious interference to other neighbor user equipments due to a channel change according to mobility and a corresponding variation of signal loss. Moreover, in viewpoint of a user equipment using a signal booster, power may be consumed unnecessarily.